Method of continuously casting plate with textured surface

ABSTRACT

Decorative plate or sheet having an attractive textured surface is continuously cast in an open ended chilled mold. The freezing plate ingot has a surface solidified in a varying and cyclic fashion by applying thereto a volatile lubricant at a rate much higher than that normally employed in similar casting arrangements. The resulting plate exhibits a textured surface with accompanying variations in composition and metallurgical structure such that the response to electrolytic anodizing treatments varies and the anodized surface exhibits varying shades and colors.

United States Patent Howle 1March 20, 1973 [54] METHOD OF CONTINUOUSLY 3,329,200 7/1967 Craig .Q. ..l64/268 CASTING PLATE WITH TEXTURED 3,630,266 12/1971 Watts ..l64/73 SURFACE Primary Examiner-R. Spencer Annear [75] Inventor. Element Roger Howle, Murrysville, Atwmey Carl R. pp

[73] Assignee: Aluminum Company of America, 57 ABSTRACT Pittsburgh, Pa. Decorative plate or sheet having an attractive textured [22] Flled: 1971 surface is continuously cast in an open ended chilled 21 1 N 200 32 mold. The freezing plate ingot has a surface solidified in a varying and cyclic fashion by applying thereto a Related Application Data volatile lubricant at a rate much higher than that nor- [62] Division of Ser. No. 23,205, March 27,1970. employed in Similar casting arrangements- The resulting plate exhibits a textured surface with accom- [52] us. Cl ..l64/73, 164/82 pany g ariatio n mpositi n and metallurgical [51] Int. Cl. ..B22d 11/00 structure such that the response to electrolytic anodiz- [5 8] Field of Search ..l64/73, 82, 268, 281 ing treatments varies and the anodized surface exhibits varying shades and colors.

[56] References Cited 6 Claims, 5 Drawing Figures UNITED STATES PATENTS 3,286,310 1l/l966 Dore et al 164/281 [(2 2/4 /6 I 3/ l4 I I h :I a2 26 27 29 E'EE' :1 O i1 l j I I:

PRTENT-EDmz 0191a SHEET 2 BF 3 FIG. 3

FIG. 4

METHOD OF CONTINUOUSLY CASTING PLATE WITH TEXTURED SURFACE This is a division of application Ser. No. 23,205, filed Mar. 27, 1970.

BACKGROUND OF THE INVENTION Aluminum and aluminum alloy members in various configurations have found wide acceptance in the architectural, furniture and other fields. Many of these members develop their own color in an anodic coating treatment which not only saves the expense of dyeing or otherwise coloring the coating but results in a more durable color. The invention provides a plate product which exhibits what may be called a surface which is rippled or randomly textured but which is very rich in appearance and quite attractive especially when viewed from some distance as on a building or a wall, inside or outside. The improved plate, when anodized in a manner which produces an integrally developed colored anodic coating, exhibits varying hues or color shades between the outer faces and the lower faces of the ripples which presents an extremely attractive appearance.

DESCRIPTION The invention is best understood by reference to the figures in which:

FIG. 1 is an elevation view, in cross section, showing a horizontal casting arrangement suitable in practicing the invention;

FIG. 2 is an elevation in cross section showing a portion of the arrangement in FIG. 1 on an enlarged scale;

FIGS. 3 and 4 are photomicrographs taken at sections across the anodic coating and adjacent metal substrate of the improved plate product after anodizing; and

FIG. 5 is'a photograph showing a typical example of the improved plate, illustrating its textured surface.

Referring now to FIGS. 1 and 2, there is shown an arrangement suitable in producing the improved cast plate in accordance with the invention employing a horizontal open ended mold. Chamber holds a body of molten metal 12 adjacent chilled mold 14 but separated therefrom by a refractory plate member 16 having an opening 18 therethrough to admit molten metal from the supply body 12 into the chilled mold. Water or other coolant is circulated within the chilled mold through passages 20 to solidify the molten metal to produce cast plate 22 which is continuously removed by withdrawal means not shown. External cooling means, not shown, may be employed to further cool the cast plate if such is desired. The surface 24 of the molten metal supply body 12 is maintained at some height above the upper surface 26 of the ingot by some distance h so that molten metal within the mold is under a slight hydrostatic head or pressure. A lubricant is applied to the freezing metal surface to reduce friction between the mold and solidifying shell which can I otherwise cause tearing. Accordingly in the particular embodiment pictured in FIGS. 1 and 2 there is provided an oil chamber 30 extending across the mold width. 'As described in more detail in US. Pat. No.

' 3,381,741 oil is supplied to oil chamber 30 under some amount. of pressure and is conducted through a plurality of passageways 32 which may be, as explained in the patent just mentioned, provided as a series of grooves which are closed by an insert member 34 to complete the passageways 32.

In practice of the invention lubricant oil is applied to the freezing metal surface in copious amounts, the rates being much greater (even by an order of magnitude) than those usually associated with continuous casting. The particular lubricant employed should be somewhat volatile such that, in the amounts employed, it vaporizes to form vapor bodies or pockets ofsignificant number and size. This intermittently alters the rate of heat extraction, which is greatly reduced at the local sites of vapor pockets, from point to point in the mold and results in a solidification rate which for any given mold portion varies or alternates from higher to lower levels in a repetitive manner. The alternating solidification rate produces the desired variations in surface condition. The rates contemplated are about 0.1 to 2 ml lubricant per minute per inch of mold periphery although a maximum of 1 ml is preferred for best results. Using a rate of about 0.3 to 0.6 ml/min/in has proved quite satisfactory in some embodiments, especially those employing horizontal casting techniques.

In horizontal casting the solidification effects on the upper and lower surfaces are not identical although both respond to the conditions here described. The response to the cyclic solidification effects is more pronounced on the upper surface than the lower surface and it is advantageous to employ the techniques here described on this surface since it is easily visible and readily controlled.

The rate at which the lubricant is applied may be constant or it can be varied, although it need not be varied in order to achieve the alternating solidification effect. If the oil rate across only one surface of the cast plate is specially controlled, e.g., the upper surface where casting horizontally, such might require a separate lubricant channel 31 for that surface. Also it might be advisable to provide a number of separate chambers across the mold width in order to assure the desired lubricant application rate across the entire textured surface especially where the plate is of substantial width. Another advantage of the separate oil compartments is that the rate can be regulated within the desired limits to result in different freezing patterns across the ingot width if such is desired. While the lubricant may be applied at a substantially constant rate it can, if desired, by changed to produce differing textures or patterns along the length of the cast plate if this particular effect is desired.

Typical lubricants contemplated in practicing the invention include castor oil and castor oil derivatives, diesters and rape-seed oil. The main requisites are stability from the standpoint of freedom from de-composition and that the oil be volatile, that is, it must have an appreciable vapor pressure at the temperatures to which the oil will be used as it is applied to the surface of the freezing ingot. These temperatures normally range from 600 to 900F and, accordingly, the oil should have a vapor pressure at these temperatures which assures the production of a substantial volume of oil vapor.

One factor which appreciably effects the freezing pattern and the resulting surface texture is casting speed. A higher rate of casting results in a relatively open texture whereas a slower speed tends to produce a closer, that is, more closely spaced, texture. For instance increasing the rate 3 inches from 24 to 27 inches per minute can produce an enormous difference in texture or pattern. Hydraulic head, h in FIG. 1, is also quite significant in that, for a given casting rate, a variation of 1 inch can product a substantial difference in texture with larger head levels resulting in closer textures. In general the hydraulic head should be maintained between 1 and 10 inches.

In introducing the molten metal into the chilled mold it is desirable that the liquid metal be presented to the mold at a substantially uniform temperature across the mold width, especially for plate thickness one-half inch and under. Presenting the molten metal at a temperature which does not vary by more than plus or minus 5F across the entire width of reservoir in the vicinity of gate opening 18 is satisfactory.

The plate produced in accordance with the invention can range from about one-sixteenth to about 1 inch although plate thicknesses ranging from about oneeighth to about one-fourth or one-half inch are usually more useful in decorative plate applications and accordingly may be considered preferred. In this connection it is considered worth mentioning that the term plate as herein used is not intended to be restrictive with respect to sheet, strip and other similar shapes. It applies to any generally planar shape and, in a sense, contemplates both sheet and plate where such are defined separately in terms of thickness dimension. The plate width can vary widely, from less than 1 foot up to 4 feet or more being typical. The improved cast plate has a surface texture quite pleasing to the eye. It exhibits a very attractive series of bands or ripples extending generally laterally across all or a portion of the plate width. FIG. 5 shows a typical example of the improved plate, with the plate width running across the figure and the casting direction being vertical in the figure. In this particular instance the lateral extremities of the plate (those near the edges of the plate width) have a surface condition characterized by a fairly uniform pattern of laterally disposed ripples (normal to the casting direction). The central portions of the plate width, however, exhibit a surface pattern which is much more open and random. If desired the central portions of the plate can be imparted with the closer texture of the edge portions simply by reducing the casting speed and increasing the lubrication rate. A photograph of such a plate surface is suggestive of a small portion of a giant fingerprint. However, when viewed at a distance of ten or fifteen feet the plate loses this effect and appears quite attractive. It can be appreciated, of course, that the attractiveness of a particular pattern is largely a matter of individual choice. Following the basic guides here set forth does, however, allow adjustments in the surface texture to suit a particular choice.

The distance (normal to the surface) between the outer or upper faces (the peaks) 27 in FIG. 1 and the lower or inner faces (valleys) 29 typically amounts to about 0.005 inch although variations of up to 0.02 inch are readily produced. The faces traverse a substantial portion of the ingot plate width and may traverse substantially the entire width. The distance across the outer and inner faces, the distance along the cast length, typically varies from 0.060 for a close texture to an inch or several inches for a more open texture and the outer and inner faces may or may not be substantially equal in dimension. Typically the outer and inner faces are more or less flat and parallel to the mold axis as shown in FIG. 1 although such is not always the case and the invention also contemplates oblique, curved and other faces. It should be noted that the rectangularity and spacing of the faces 27 and 29 in FIG. 1 is exaggerated for emphasis.

The textured plate surface when anodized will produce variations in shading and color contrasting the outer and inner faces as best illustrated in FIG. 5. The extent of the contrast and variation is largely dependent on anodizing conditions and the plate composition together with the extent of the variation in the alternating freezing condition.

From the standpoint of metal composition, the invention especially contemplates the use of aluminum alloys whose anodic color response varies according to the rate of surface solidification. This is usually a function of the constituent size and distribution and accordingly, the invention mainly contemplates the use of alloys having a significant amount of constituent. However, even substantially pure" alloys usually have some amount of impurities present which form some sort of constituent. For instance, 1100 alloy, which refers to a composition containing at least 99 percent aluminum, responds to the improved practice although to a somewhat lesser extent than alloys containing greater amounts of alloy constituents. One alloy which is quite suitable in practicing the invention contains 3 to 13 percent silicon. In addition, it can contain small amounts of magnesium, chromium and copper such as it may include up to 1 percent Mg, up to 0.7 percent Cr and up to 0.7 percent Cu. These additions, while adding to the strength of the plate, are used primarily for their color producing effects in integrally developed anodic coatings. Especially suitable for some applications is an alloy containing 3 to 7 percent Si and 0.4 to 0.6 percent Cr. This alloy produces very attractive shadings of greys and golds in response to anodizing treatments.

To demonstrate the variation in color and shade response to composition a number of alloy compositions were cast into plate three-sixteenths inch thick using a horizontal continuous casting procedure. The casting rate was about 32 to 36 inches per minute and the molten metal entered the mold under a hydraulic head of about 5 inches. Lubricating oil was applied to the upper surface at a rate within the range of about 0.3 to 0.6 ml per minute per inch of surface width. Table I lists the amount of alloy additions included in each composition.

TABLE I Composition Si Cr Mg Cu l 6 0.5 2 7 0.25 0.08 3 12 These plates I were anodized in a bath containing about 16 percent sulfuric acid at a temperature of F and a current density of 12 amps per sq. ft. for 45 minutes. Reflectance was measured using a Photovolt Reflection Meter No. 670. (Reference U.S. Dept. of Commerce, National Bureau of Standards C429 Titled Photoelectric Tristimuluii Colorimetry with Three Filtens," By R. S. Hunter, Issued July 30, 1942.)

Table II sets forth the coating thickness and the apparent reflectance (percent AR) contrasting the light areas and the dark areas in the plate together with an indication of the visual effect observed which is listed as a major color with color overtones in parenthesis.

TABLE II Compo- Coating Light Areas Darker Areas sition Thick- AR Visual AR Visual ness 1 0.7 mi] 17.0 Silver 6.4 Charcoal (yellow & grey gold) (gold &

brown) 2 0.9 mil 1 1.4 Silver 3.6 Charcoal (blue & (blue & grey) brown) 3 0.9 mil 6.6 Brown 4.8 slate (bronze) Improved cast plate containing 7 percent Si was used for micrographic analysis. The plate exhibited lighter and. darker areas of a generally bronze-like color. The micrographs showed pronounced differences between the lighter and darker portionsof the anodic coating and their associated substrates. The light colored portions exhibited an average Si constituent particle size of about 0.00017 inch and only an average of four such particles per cubic mil (mil 0.001 inch). This effect results from a relatively slow rate of surface solidification which generally prevailed in the inner face 29 regions. The dark colored region exhibited a constituent particle size of 0.00007 inch but the number of particles was greatly increased to from about 300 to about 350 per mil and this region exhibited a generally salt and pepper appearance. This effect results from a relatively rapid surface solidification rate which characterizes the outer faces 27. These respective effects are shown in FIGS. 3 and 4 wherein FIG. 3 shows the lighter color region of the inner faces and FIG. 4 the darker color region.

It is noteworthy that the outer faces 27 are usually the darker faces upon integral color development in anodic oxidation as is clearly the situation with aluminum alloys containing silicon. However, such is not always the case. Plate about one-fourth inch thick of alloy 3003 which contains nominally 1.2 percent Mn, 0.12 percent Cu, the balance aluminum was cast according to the invention and anodized in a sulfuric acid type of electrolyte. The surface developed shades of a metallic pink which varied from a fairly light pastel shade in the outer faces to a pink and silver grey speckled shade in the inner faces. In the transition slopes between the outer and inner faces the color was generally a silver grey with a pinkish hue.

From the foregoing illustrations it is apparent that the color and contrast of the lighter and darker faces can be varied widely in practicing the invention. It is especially significant that these effects are achieved in a controlled and repeatable manner. To appreciate the unique character of the improved plate the situation where a mating mold is fashioned by molding plaster or figuration of the improved late roduct. However, the p ate cast in the plaster ma e mo d does not exhibit the controlled variation in surface substrate structure which characterizes the improved plate product. Accordingly, when the plaster mate mold cast plate is anodized, it does not exhibit the desired color and shade variations which characterize the improved plate product.

While the invention is described in certain preferred embodiments or in certain embodiments highly suited to particular applications such is not intended to constitute limitations in construing the invention described and claimed which is intended to encompass all embodiments falling within the spirit of the invention. For instance, while the invention is described with particular reference to horizontal casting it would be applicable to other types of continuous casting which would be expected to produce similar results.

What is claimed is:

l. A method of horizontally continuously casting plate composed of an aluminum alloy, the plate ranging in thickness from about one-sixteenth to 1 inch comprising:

l. maintaining a body of molten metal adjacent an open ended horizontal continuous casting mold,

2. continuously introducing said molten metal into said mold and withdrawing a solidified ingot plate therefrom,

3. applying to a surface of said metal a volatile lubricant at a rate of from 0.1 to 2 ml per minute per inch of surface width to cause the intermittent formation of lubricant vapor pockets to effect alternating higher and lower solidification rates in said surface thereby producing in said surface a texture having multiplicities of outer and inner faces, the outer faces having internal structural characteristics derived from a more rapid solidification rate than the inner faces, whereby to produce in said upper surface a texture having multiplicities of higher and lower faces having different constituent distribution patterns.

2. The method according to claim 1 wherein the lubrication rate and the casting rate are maintained substantially constant.

3. The method according to claim 1 wherein said lubricant rate ranges from 0.3 to 0.6 ml per minute per inch.

4. The method according to claim 1 wherein said upper surface has applied thereto an integral anodic coating.

5. The method according to claim 1 wherein said aluminum alloy contains from 3 to 13 percent silicon.

6. The method according to claim 5 wherein said alloy additionally contains one or more of the elements selected from the group consisting of up to 1 percent Mg, up to 0.7 percent Cr and up to 0.7 percent Cu. 

2. The method according to claim 1 wherein the lubrication rate and the casting rate are maintained substantially constant.
 2. continuously introducing said molten metal into said mold and withdrawing a solidified ingot plate therefrom,
 3. applying to a surface of said metal a volatile lubricant at a rate of from 0.1 to 2 ml per minute per inch of surface width to cause the intermittent formation of lubricant vapor pockets to effect alternating higher and lower solidification rates in said surface thereby producing in said surface a texture having multiplicities of outer and inner faces, the outer faces having internal structural characteristics derived from a more rapid solidification rate than the inner faces, whereby to produce in said upper surface a texture having multiplicities of higher and lower faces having different constituent distribution patterns.
 3. The method according to claim 1 wherein said lubricant rate ranges from 0.3 to 0.6 ml per minute per inch.
 4. The method according to claim 1 wherein said upper surface has applied thereto an integral anodic coating.
 5. The method according to claim 1 wherein said aluminum alloy contains from 3 to 13 percent silicon.
 6. The method according to claim 5 wherein said alloy additionally contains one or more of the elements selected from the group consisting of up to 1 percent Mg, up to 0.7 percent Cr and up to 0.7 percent Cu. 